1. Field of the Invention
The present invention relates to a technology for feeding a recording medium from a stack of recording media one by one.
2. Description of the Related Art
In recent years, to meet various needs of customers, there has been an increasing demand for image forming by using a recording medium having high adhesiveness, such as a coated paper, an art paper, or a film sheet. However, because it is not easy to separate the sheets having high adhesiveness from one another, if a conventional feeding method using a separating claw, a separating pad, and a feed and reverse roller (FRR) is used for feeding the sheets from a sheet tray, plural sheets may be fed from the sheet tray at one time, or no sheet may be fed from the sheet tray.
To solve the above problem, in a conventional feeding device, air is blown to upper side portions of a pile of sheets stacked on a sheet tray to separate the sheets from one another, and then the sheets are fed from the sheet tray one by one (hereinafter, such a process is referred to as “air-separation feeding process”). To perform the air-separation feeding process, air inlets are arranged on side fences of a sheet tray, and the air is blown from blower fans through the air inlets to both sides of the pile of the sheets (hereinafter, referred to as “blowing operation” as appropriate). Thus, the stacked sheets are separated from one another and the sheets are then fed from the sheet tray one by one (see, for example, Japanese Patent Application Laid-open No. 2001-354331 and Japanese Patent Application Laid-open No. 2006-264917).
In Japanese Patent No. 3475716, a feeding method is disclosed in which plural sheet trays are arranged, and if it is detected that the number of sheets stacked on the current sheet tray that currently performs a feeding operation is less than a predetermined number, an air supplying unit of the next sheet tray is activated. Then, if it is detected that there is no sheets in the current sheet tray when a predetermined time elapses after the air supplying unit is activated, the next sheet tray is set to the current sheet tray, so that the next sheet tray continues to perform the feeding operation.
It has been required to perform an image forming process on a large number of sheets at a high speed. To meet such a requirement, a conventional image forming apparatus includes a plurality of sheet trays, and performs a feeding operation by switching over the sheet trays from one to another.
If the number of sheet trays is increased to feed a large number of sheets, an operation of controlling the sheet trays becomes complicated. For example, if the image forming apparatus includes two sheet trays, one is set to the current sheet tray that currently performs the feeding operation, and the other is set to the next sheet tray that will continue to perform the feeding operation next to the current sheet tray. However, if the image forming apparatus includes three or more sheet trays, the next sheet tray cannot be easily determined from among the sheet trays other than a sheet tray that is set to the current sheet tray.
Furthermore, a conventional image forming apparatus includes multiple control units (processors), and the control units operate in conjunction with each other. The same control unit is not necessarily used to determine a sheet tray from which a sheet is fed, to control a feeding operation and a conveying operation of a sheet tray, and to control the air-separation feeding process. Therefore, in some cases, the control unit has to control the air supply operation without having any information about the next sheet tray.
In such a case, it is possible that the air supply operation is started in advance in all of the sheet trays. However, if all air supplying units of the sheet trays are driven, electric-power consumption is increased. Furthermore, in some cases, sufficient electric power cannot be obtained for driving all the air supplying units depending on a capacity of a power source circuit.